1. Field of the Invention
The present invention in general relates to a display technology of a computer system, more specifically, to a computer system that can prevent abnormal display aspect and display position on a monitor due to changing of the display mode in the computer system and can automatically adjust the display aspect and the display position in accordance with the various display modes applicable to the monitor.
2. Description of the Prior Art
FIG. 1 (Prior Art) illustrates a blocking diagram of a display architecture in a conventional personal computer system. In FIG. 1, the computer system may be divided into computer 1 (the left portion of the dashed line) and monitor 60. Microprocessor 10 is a core device of computer 1, which can handle control, mathematical operation and peripheral interruption processes. Chipset 20 is used to bridge between microprocessor 10 and the Peripheral Component Interconnection (PCI) bus. In addition, microprocessor 10 can access main memory 30 via chipset 20. For Intel Pentium Pro processors, chipset 20 may be implemented by the Intel 82441FX PCI Bridge and Memory Controller (PMC) and 82442FX Data Bus Accelerator (DBX). Chipset 40 is used to control communication between the PCI bus and the ISA bus, such as the Intel 82371SB PCI/ISA IDE Accelerator (PIIX3). Video display card 50 inserted into the ISA bus is used to manipulate display information and feed video signals and accompanying synchronizing signals to monitor 60 via bus or lead 70. Video display cards may share the image-processing workload for microprocessors, thereby improving the resultant performance of the overall system. In addition to the video display cards, a dedicated image chipset installed in a motherboard may be used to perform such a function. In addition, a video display card designed for a PCI bus may be used to achieve high-speed data transmission.
Synchronizing signals and video signals indicate the display appearance and display details of monitor 60. Synchronizing signals, including a horizontal synchronizing signal and a vertical synchronizing signal, are directly or indirectly fed into a deflection circuit of monitor 60, controlling an electron beam gun scanning the display screen of monitor 60. Video signals are used to control the brightness and the color of the scanned display screen. Traditionally, there are two approaches to controlling the deflection circuit of the monitor according to the horizontal/vertical synchronizing signals. The first approach is to reproduce vertical/horizontal blanking synchronizing signals from the original vertical/horizontal synchronizing signals, to adjust the vertical/horizontal blanking synchronizing signals in accordance with the phase of the video image, and to apply these blanking synchronizing signals to drive the deflection circuit. The second approach is to apply the original synchronizing signals from the video card to directly drive the deflection circuit. Thereupon, currents flowing through the horizontal/vertical deflection yokes are modified in accordance with the present video image. Basically, both of these approaches can modify the display aspect and the display position of the monitor.
The video signals transmitted from video display card 50 to monitor 60 include red, blue and green color signals. The synchronizing signals include the horizontal synchronizing signal and the vertical synchronizing signal. In a non-interlaced display mode, a picture frame defined by the vertical synchronizing signal is composed of a plurality scanning lines defined by the horizontal synchronizing signal. FIG. 2 (Prior Art) depicts timing diagrams of a video signal and a corresponding synchronizing signal. In FIG. 2, the depicted video signal represents image data in a picture frame when the depicted synchronizing signal is the vertical synchronizing signal. In addition, the depicted video signal represents image data in a scanning line when the depicted synchronizing signal is the horizontal synchronizing signal. The timing relation between the video signal and the synchronizing signal depicted in FIG. 2 is described as follows. Symbol A denotes the synchronizing pulsed time, and the time period between the two neighboring synchronizing pulses is defined as the total time of a picture frame or a scanning line. Symbols B and F denote the back porch time and the front porch time, respectively. Front porch time F, synchronizing pulsed time A and back porch time B are called a blanking time. The blanking time is used to define the flyback time when an electron beam gun finishes a scanning line or a picture frame and then restarts a next scanning line or a next picture frame. The color setting of the video signal corresponding to the flyback time must be darkest, preventing the electron beam gun from lighting the display screen during this period. Symbols C and E denote a left/upper frame edge time or a right/lower frame edge time. Symbol D denotes the addressable time, defining the period of image data to be displayed on the monitor. Periods C, D and E are called an active video time.
Practically, various video display cards fabricated by different manufacturers may output different video signals (red, green and blue) and synchronizing signals (horizontal and vertical). To bridge such differences, the Video Electronics Supplier Association (VESA) has proposed a set of standardized synchronizing parameters for various display modes. For example, the proposed synchronizing parameters for a display mode with a vertical scanning frequency of 72 Hz and a display resolution of 640.times.480 pixels are listed as follows:
Horizontal scanning:
total scanning time: 26.413 .mu.sec; PA1 synchronizing pulsed time: 1.270 .mu.sec; PA1 front porch time: 0.508 .mu.sec; and PA1 back porch time: 3.810 .mu.sec; PA1 total scanning time: 13.735 msec; PA1 synchronizing pulsed time: 0.079 msec; PA1 front porch time: 0.026 msec; and PA1 back porch time: 0.528 msec.
Vertical scanning:
These proposed display modes have different timing specifications for various combinations of video display cards and monitors. Theoretically, if all video display cards fabricated by various manufacturers comply with these standardized specifications proposed by VESA to output the video signals and the synchronizing signal, the monitors may previously store a plurality of sets of display parameters corresponding to these display modes and retrieve them as required, optimizing the display aspect and the display position. Related technologies, such as display modes, parameter storing and parameter retrieving, have been disclosed in U.S. Pat. No. 5,021,713, "Display," Arai et al., and will not be further described.
At present, however, most of the video display cards do not completely conform with the proposed standardized specifications, except for the definition of the picture resolution in the active video time. This is the result of various practical considerations, such as technical capability and production cost. Since the timing characteristics of the video signals and the synchronizing signals generated by various video display cards are quite different, a step for manually modifying the display aspect and the display position must be taken to adjust the timing parameters when a display configuration has been altered.
Some commercial monitors provide an automatic adjustment function to solve the problems caused by manually adjusting the monitor, such as errors caused by manual adjustment and the extra cost of adding an additional adjusting circuit. The automatic adjustment function optimizes the monitor display by the following steps. First, the active video time is determined by an auto-detection technique. The detected active video time is used to determine the front porch time and the back porch time. Then the timing relation between the active region and the front/back porch times is modified to meet the standardized specifications by calculating the front porch time, the synchronizing pulsed time and the back porch time.
However, such an automatic adjustment means does not work in some circumstances. The active video time of the video signals may not carry enough image data that can be detected by the above-indicated auto-detection technique. For example, in a text mode of the DOS environment, the visible region of the monitor is merely a portion of displaying a prompt or input/output letters. It is evident that a portion of the active video time of the video signals does not contain any image data and cannot be detected. On the other hand, in a graphic mode of the Windows environment, the whole active video time of the video signals is visible. Therefore, an abnormal display may occur owing to the auto-detection technique when the computer system is operated in the DOS environment, and display modes or the operation environment (such as switching from the Windows environment into the DOS environment) are changed.
FIG. 3A (Prior Art) depicts a display screen of a computer system operated in a graphic environment (such as the Microsoft Windows environment) and FIG. 3B (Prior Art) illustrates timing diagrams of the corresponding video signal and synchronizing signal. In this case, the video signal has detectable image data during the active video time (including front/back edge times and addressable time). Therefore, a monitor using the conventional auto-detection technique can exactly detect the front porch time and the back porch time. On the other hand, FIG. 3C (Prior Art) depicts a display screen of a computer system operated in a text environment and FIG. 3D (Prior Art) illustrates timing diagrams of the corresponding video signal and synchronizing signal. It is evident that the image data carried by the shown video signal do not completely occupy the defined active video time. Therefore, errors may occur when detecting timing characteristics. Accordingly, conventional auto-detection technique cannot achieve the purpose of automatically modifying the display aspect and the display position.